Active matrix displays employ a switch at each picture element in a matrix display so that the voltage across each pixel can be controlled independently. Active matrices are especially suitable for high information content Liquid Crystal Displays (LCDs) such as LCDs used in second-generation PDAs and cell phones.
Other types of displays that typically require a switching device at each picture element include Electrophoretic Displays (EFDs) and rotating element displays. Electrophoretic displays, including displays available from companies such as E-Ink and Sipix, produce an image relying on translational movement of charged colored particles suspended in a liquid of a different color. Rotating element displays use rotational movement of optically and electrically anisotropic elements, such as bichromal spheres having a non-uniform charge distribution. Pixel performance of electrophoretic and rotating element displays can be controlled with a switching device that provides on- and off- voltages to each of the picture elements in the display matrix.
Switching devices that have been proposed for active matrix display applications include various types of Thin Film Transistors (TFTs) and Thin Film Diodes (TFDs) such as Metal Insulator Metal (MIM) diodes. MIM diodes are particularly appealing since their structure is relatively simple and they are typically easier to fabricate than TFTs.
MIM diodes are broadly defined as switching devices that include a layer of an insulating or semiconducting material residing between two layers of conductive material (not necessarily metal). Often MIM devices do not include any other layers beyond these three layers; however this is not necessarily the case. Regardless of the specific structure, fabrication of MIM devices at particular levels of miniaturization can be still a laborious and expensive process. Typically, MIM devices are fabricated using techniques employed in integrated circuit industry requiring costly equipment and laborious processing.